Need tips on drilling a long thin through hole

[tjb]

I need to drill two holes in a piece of 5/8" aluminum that measures 2" x 4 1/8". The holes need to be 3/16" and go through the 4 1/8" length. They need to be very accurate, so I plan on doing the operation on my mill.

I have found several bits to choose from but don't know what parameters to select (material, point angle, etc.).

I've never tried to drill a hole that deep and narrow, and life would be difficult if the bit breaks off in the hole. Any tips to help avoid a catastrophe? Drill speed/feed rate/etc.?

Thanks in advance.

Regards,
Terry

 

[Z2V]

Could you drill from both ends and meet in the middle?

 

[tjb]

Could you drill from both ends and meet in the middle?

Thought about it. Would rather avoid it because that would introduce a potential misalignment. I see that as a worst case scenario solution that I hope I can avoid.

Thanks

 

[mmcmdl]

Guhring parabolic drill would work nicely .

 

[tjb]

Guhring parabolic drill would work nicely .

Any one in particular? MSC Direct lists 12 of them. They range from about $15 to $476 with all kinds of different parameters.

Thanks

 

[Bob Korves]

Good luck, TJB. I would not want to try that one if the drill must stay closely accurate to the center line. Someone who does gun barrel boring might have the best advice...

 

[mmcmdl]

Yes , they are expensive . If you have their big book they explain what performs best for special applications . I don't have the book in here at work . They make deep hole drills for aluminum though , one of my past jobs required drilling 12" deep thru aluminum for a drone antenna ( SP ) . I pecked it on a cnc lathe with no problem .

 

[tjb]

Good luck, TJB. I would not want to try that one if the drill must stay closely accurate to the center line. Someone who does gun barrel boring might have the best advice...

Thanks, Bob.

Hopefully one of our riflemen will offer some advice.

Regards,
Terry

 

[tjb]

Yes , they are expensive . If you have their big book they explain what performs best for special applications . I don't have the book in here at work . They make deep hole drills for aluminum though , one of my past jobs required drilling 12" deep thru aluminum for a drone antenna ( SP ) . I pecked it on a cnc lathe with no problem .

Wonder if I could improve my odds of success by starting with a 64th under screw machine or jobber bit. Then following with the extended length?

Anyone?

Thanks,
Terry

 

[mmcmdl]

When you state " needs to be very accurate " , regarding diameter , true position , parallelism ? All of the above ?